The invention relates to dispensing systems for providing an automatic discharge of a chemical to a liquid stream. For example, it is often desirable to be able to treat water streams associated with cooling towers, heat exchangers, evaporative condensers, etc. to control various problems such as microbiological fouling, corrosion and scale. Although very large installations often have very sophisticated treatment systems and regularly scheduled maintenance, there are many somewhat smaller systems which could operate without maintenance for a few weeks to a few months if a relatively small quantity of treatment chemical were added to them on a uniform basis during their hours of operation. Examples of prior art systems for dispensing chemicals contained in solid briquettes are found in Hunsaker U.S. Pat. No. 3,430,823 as well as in Gilwood U.S. Pat. No. 3,385,483 and Currie U.S. Pat. No. 3,094,134. Each of these systems permits the bottom briquette in a stack to be intermittently contacted and partially dissolved as the water level in a feed chamber cyclically rises and is then emptied by a siphon tube. Although the briquette type units perform quite satisfactorily, the briquettes are expensive to manufacture and restrict somewhat the ability to provide a wide range of suitable chemicals and concentrations. Liquid chemicals are more satisfactory in the latter respects, but existing commercial units utilize drip feeders which can be difficult to start, which are relatively expensive, and which can become very difficult to reuse if the feed bottle is allowed to completely drain so that crystals have a change to form. Also, such feeders are wasteful if they continue to provide chemicals when the unit whose water is being treated is not operating. U.S. Pat. No. 2,461,334 shows a system for siphoning a treatment chemical into a feed chamber, but appears to be quite sensitive to changes in viscosity with temperature, and uses a tube to meter a desired amount of chemical.